This research is based on the overall hypothesis that non-collagenous extracellular matrix (ECM) proteins made by odontoblasts play a vital role in the formation of dentin. Dentin is formed when odontoblasts secrete a collagen-rich ECM that mineralizes in a highly controlled manner. Dentin ECM proteins, secreted by odontoblasts coincident with the formation of the initial predentin layer, closely resemble ECM proteins made by osteoblasts, which are implicated in osteogenesis and bone homeostasis. However, at least two of the dentin proteins are uniquely expressed by odontoblasts and not by other mineralized tissue cells. These two proteins, dentin phosphoprotein (DPP) and dentin sialoprotein (DSP), are the subjects of this application. Thus, studies are described to study the nature, cellular expression and gene structure and regulation of DPP and DSP. The specific aims of this proposal are 1) to study the chemical nature, biosynthesis and secretion, gene structure and regulation and potential function of DPP, 2) To study mouse DSP and DSP gene sequence and organization, regulation of synthesis and potential function, and 3) To develop a null mutant DSP mouse for studying the biological function of DSP. It is expected that the results of the ongoing studies in the Principal Investigator's laboratory will bring about a better understanding of how dentin and other mineralized tissues form.